At present, the lithological composition of a rock being drilled is determined by obtaining a sample of the rock by a core bit and subsequently analysing the texture and mineralogical composition of the rock. This technique is characterized by its time- and labour-consuming character, and, hence, by its high cost.
There are also widely known methods of determining the tectonics, structure and lithology of rock with aid of electric-logging charts obtained by conducting electric logging while drilling a borehole or well. The methods are likewise characterized by their highly labour-consuming character, because in order to conduct the logging, the drilling tool has to be pulled out of the borehole, the appropriate instruments have to be run into borehole on the cable, and the data obtained has to be subsequently interpreted and analysed.
There are further known methods of determining the lithological composition of the rock in a borehole by using the drilling cuttings entrained in the upward flow of the drilling mud. The drilling cuttings are employed according to these methods for determining the texture and the mineralogical composition of the rock strata traversed by the borehole, by using laboratory methods.
However, these last-mentioned known methods are characterized by the insufficiently accurate information they yield, since it cannot be always positively known to which traversed stratum these or other drilling cuttings belong, to say nothing of the considerable time it takes to investigate the mineralogical composition of the samples of the drilling cuttings.